november 3, 2008 handout

1. Transcription: DNARNA; instructions that are performed to make proteins
a. Gene expression: whether particular gens are transcribed and translated at one time and other times they are not Ex: why don’t V. fischeri always glow?
b. Entire genome is NOT transcribed all the time; only particular genes
c. Genes: a sequence of DNA that codes for one particular protein
d. Steps of transcription
i. Initiation
1. Transcription makes ssRNA copy of DNA gene in order to do this, strands of DNA must be uncoiled and unzipped
a. RNA polymerase (enzme) copies DNARNA
i. Different versions (sigma factors) of subunit (sigma subunit) initially bind to DNA based on the particular sequence of the bases
b. Promoter sequence: sequence of DNA bases the RNA polymerase sigma subunit initially binds to so the RNA polymerase start unwinding and unzipping DNA
c. Change in genome expression can be caused b change in what sigma factors bacteria make in different conditions
i. Ex: E. coli make different sigma factors at high vs. low temperaturesdifferent gene expression at different temperatures
ii. Elongation
1. RNA polymerase reaches gene beginning, starts bringing in RNA bases complementary to ssDNA sequence, hooks bases into chain w/ sugar-phosphate backbone
a. Sugar-phosphate backbone has ribose-phosphate
b. RNA uses uracil, not thymine
iii. Termination

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